<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>

	<body>

		<li id="item">
			<span id="span">我是span</span>
			<button id="btn">我是button</button>
		</li>
		<p>
			<button onclick="move();">移动</button>
		</p>
	</body>

</html>

<script type="text/javascript">
	function move() {
		var li = document.getElementById('item');
		var span = document.getElementById('span');

		li.appendChild(span);
	}
</script>